The 2016 Great Barrier Reef heatwave caused widespread changes to fish populations

Some fish fared better than others amid the extreme temperatures of the 2016 heatwave.
Rick Stuart-Smith/Reef Life Survey

Rick Stuart-Smith, University of Tasmania; Christopher Brown, Griffith University; Daniela Ceccarelli, James Cook University, and Graham Edgar, University of Tasmania

The 2016 marine heatwave that killed vast amounts of coral on the Great Barrier Reef also caused significant changes to fishes and other animals that live on these reefs.

Coral habitats in the Great Barrier Reef (GBR) and in the Coral Sea support more than 1,000 fish species and a multitude of other animals. Our research, published in Nature today, documents the broader impact across the ecosystem of the widespread coral losses during the 2016 mass coral bleaching event.

While a number of fish species were clearly impacted by the loss of corals, we also found that many fish species responded to the increased temperatures, even on reefs where coral cover remained intact. The fish communities in the GBR’s southern regions became more like those in warmer waters to the north, while some species, including parrotfishes, were negatively affected by the extreme sea temperatures at the northern reefs.

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Read more:
How the 2016 bleaching altered the shape of the northern Great Barrier Reef

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The loss of coral robs many fish species of their preferred food and shelter. But the warming that kills coral can also independently cause fish to move elsewhere, so as to stay within their preferred temperature range. Rising temperatures can also have different effects on the success, and therefore abundance, of different fish populations.

One way to tease apart these various effects is to look at changes in neighbouring reefs, and across entire regions that have been affected by bleaching, including reefs that have largely escaped coral loss.

We were able to do just this, with the help of highly trained volunteer divers participating in the Reef Life Survey citizen science program. We systematically surveyed 186 reefs across the entire GBR and western Coral Sea, both before and after the 2016 bleaching event. We counted numbers of corals, fishes, and mobile invertebrates such as sea urchins, lobsters and giant clams.

Sea temperatures and coral losses varied greatly between sites, which allowed us to separate the effects of warming from coral loss. In general, coral losses were much more substantial in areas that were most affected by the prolonged warmer waters in the 2016 heatwave. But these effects were highly patchy, with the amount of live hard coral lost differing significantly from reef to reef.

For instance, occasional large losses occurred in the southern GBR, where the marine heatwave was less extreme than at northern reefs. Similarly, some reefs in the north apparently escaped unscathed, despite the fact that many reefs in this region lost most of their live corals.

Sea temperatures the culprit

Our survey results show that coral loss is just one way in which ocean warming can affect fishes and other animals that depend on coral reefs. Within the first year after the bleaching, the coral loss mostly affected fish species that feed directly on corals, such as the butterflyfishes. But we also documented many other changes that we could not clearly link to local coral loss.

Much more widespread than the impacts of the loss of hard corals was a generalised response by the fish to warm sea temperatures. The 2016 heatwave caused a mass reshuffling of fish communities across the GBR and Coral Sea, in ways that reflect the preferences of different species for particular temperatures.

In particular, most reef-dwelling animals on southern (cooler) reefs responded positively to the heatwave. The number of individuals and species on transect counts generally increased across this region.

By contrast, some reefs in the north exceeded 32℃ during the 2016 heatwave – the typical sea temperature on the Equator, the hottest region inhabited by any of the GBR or Coral Sea species.

Some species responded negatively to these excessive temperatures, and the number of observations across surveys in their northernmost populations declined as a consequence.

Parrotfishes were more affected than other groups on northern reefs, regardless of whether their local reefs suffered significant coral loss. This was presumably because the heatwave pushed sea temperatures beyond the level at which their populations perform best.

Nothing to smile about: some parrotfishes don’t do well in extreme heat.
Rick Stuart-Smith/Reef Life Survey

Local populations of parrotfishes will probably bounce back after the return of cooler temperatures. But if similar heatwaves become more frequent in the future, they could cause substantial and lasting declines among members of this ecologically important group in the warmest seas.

Parrotfishes are particularly important to the health of coral reef ecosystems, because their grazing helps to control algae that compete with corals for habitat space.

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Read more:
How the 2016 bleaching altered the shape of the northern Great Barrier Reef

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A key message from our study is not to overlook the overarching influence of temperature on coral reef ecosystems – and not to focus solely on the corals themselves.

Even if we can save some corals from climate change, such as with more stress-tolerant breeds of coral, we may not be able to stop the impacts of warming seas on fish.

Future ecological outcomes will depend on a complex mix of factors, including fish species’ temperature preferences, their changing habitats, and their predators and competitors. These impacts will not always necessarily be negative for particular species and locations.

One reason for hope is that positive responses of many fish species in cooler tropical regions may continue to support healthy coral reef ecosystems, albeit in a different form to those we know today.

Rick Stuart-Smith, Research Fellow, University of Tasmania; Christopher Brown, Research Fellow, Australian Rivers Institute, Griffith University; Daniela Ceccarelli, Adjunct Senior Research, ARC Centre of Excellence for Coral Reef Studies, James Cook University, and Graham Edgar, Senior Marine Ecologist, Institute for Marine and Antarctic Studies, University of Tasmania

This article was originally published on The Conversation. Read the original article.

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Why do dingoes attack people, and how can we prevent it?

Dingoes are usually solitary, but can forage in groups near human settlements where food is abundant.
Klaasmer/Wikimedia Commons, CC BY-SA

Bill Bateman, Curtin University and Trish Fleming

The case of Debbie Rundle, who was attacked by dingoes at a mine site in Telfer, in Western Australia’s Pilbara region, evokes our instinctive horror at the idea of being attacked by wild animals.

Rundle suffered severe leg injuries in the incident, and said she feared she may have been killed had her colleagues not come to her aid.

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We know that there are carnivores throughout the world with the potential to kill us. And while most of us will never come face to face with a hungry wolf, lion, tiger or bear, such attacks do unfortunately still occur.

In the scale of things, such attacks are very uncommon – although that is little consolation to the victim. Australia’s dingoes are no exception; despite some infamous examples, dingo attacks on humans are mercifully rare. But people will still understandably want to know why they happen at all, and what can be done to prevent them.

Why do wild animals attack?

Research on wolf attacks shows that, absent the influence of rabies which can increase wolves’ aggression, two common factors associated with attacks are that they often happen in human-modified environments, and by animals that are habituated to human presence.

These two variables are obviously linked: many species of mammalian carnivore are highly adaptable, and soon learn that human settlements are sources of food, water and shelter.

These human resources can have a profound effect on the behaviour of wild animals. Abundant human food often reduces animals’ aggression towards one another, and can result in the presence of much larger numbers of individuals than normal.

This is equally true of dingoes. Although they are usually observed alone, it is not uncommon to see groups of ten or more dingoes foraging at rubbish dumps associated with mine sites in the Tanami Desert of central Australia. There are thought to be around 100 dingoes that forage in and around the Telfer mine where Rundle was attacked.

Waste food may inadvertently entice animals to human settlements, and this may lead to predators becoming habituated to human presence. In Canada, a young man fell victim to a wolf attack at a mine site; the local wolves were reported to be used to humans, and would even follow rubbish trucks to the tip. They may have come to associate human smells with the provision of food.

Animals that are habituated to humans lose some of their natural wariness towards them. This is typical of many animal species that adapt to urban habitats, and while this may be an appealing trait in squirrels or garden birds, it can be quite different if the animal is a predator capable of attacking a human.

Coyotes can be dangerous, especially when they get used to living in human environments.
Marya/Flickr/Wikimedia Commons, CC BY-SA

In the United States, there have been many reports of coyotes attacking humans. The coyote, like the dingo, is reasonably large (typically weighing 10–16kg) and can be found in close association with urban areas. The coyote’s natural range has expanded as wolves (their competitor) have dwindled, and their numbers have increased in and around cities where they find copious and consistent supplies of food and water.

A survey of reported attacks on humans by coyotes showed that many were “investigative”, often involving the animal trying to steal something they perceived as food from the person. Other attacks by coyotes could be identified as “predatory”, in which the victim was pursued and bitten, and often occurred when the coyotes were in a group.

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Dingoes do bark: why most dingo facts you think you know are wrong

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The Telfer dingo attack similarly appears to have been investigative – a young dingo climbed onto a table and grabbed Rundle’s phone. But the incident turned nasty when Rundle (perhaps understandably) followed the dingo that had her phone; this seemed to trigger a defensive or predatory attack from two other dingoes.

On Queensland’s Fraser Island, more than half of the recorded aggressive incidents by dingoes towards humans happened when the person was walking or running, suggesting that a “chase” response may have been involved.

The Telfer site, like other mine sites, has strict rules about putting waste food in bins, and managers have been proactive in training workers to not feed dingoes, in an attempt to prevent just such attacks. Rundle certainly seems to have followed these rules.

Unfortunately, in her case, other variables contributed to the attack – an investigative approach by one dingo that stole an item (that may have smelled of food) seems to have turned into an aggressive group attack when she followed the animals.

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Want dingoes to leave people alone? Cut the junk food

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What can we do to prevent such attacks? Mine site managers already do much to reduce the likelihood of such incidents by reducing dingoes’ access to food. Fencing off eating areas or storing food in cages – as is done at Fraser Island – can help in this regard.

Interestingly, many people believe that it is best not to act aggressively when they encounter a large carnivore, but in reality it depends on the species. For wolves and pumas, the best tactic seems to be to shout and throw objects to put them off.

Ultimately, the onus is on individual people to be aware of the potential danger of wild predators, and always to treat them with wariness and respect.

Bill Bateman, Senior Lecturer, Curtin University and Trish Fleming, Associate Professor

This article was originally published on The Conversation. Read the original article.

Jupiter’s new moons: an irregular bunch with an extra oddball that’s the smallest discovered so far

A moon shadow on Jupiter, the red planet now has a dozen more moons added to the list or such orbiting bodies.
NASA/JPL-Caltech/SwRI/MSSS

Jonti Horner, University of Southern Queensland and Christopher C.E. Tylor, University of Southern Queensland

Jupiter is the largest planet in the Solar system and has been studied intensively for hundreds of years, so you might think there would be little left to find.

But earlier this month, researchers announced that another 12 moons have been added to the number of such bodies orbiting the giant planet.

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The latest from Juno as Jupiter appears bright in the night sky

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That brings the tally for Jupiter to a whopping 79, the most moons for any known planet. But where did these newly discovered moons come from, and what do they tell us about Jupiter and its place in the Solar system?

Moons: regular and irregular

The Solar system’s giant planets have two types of moon: regular and irregular.

Regular moons orbit close to their host, follow nearly circular paths, and move in the same plane as the planet’s equator. In some ways, these moons resemble miniature planetary systems, and we think that they formed in much the same manner as the planets around the Sun.

As the giant planets gathered material from the disk of gas and dust that surrounded the young Sun – a process known as accretion – they were surrounded by their own miniature disks. Within those disks, the regular moons grew, all in the planet’s equatorial plane.

Artist’s impression of a protoplanetary disk – a place where planets are born. Around young giant planets, similar disks give birth to regular moons.
ESO/L. Calçada

But the irregular moons are another story.

Their orbits are highly eccentric (elliptical) and inclined relative to the plane of their host planet’s equator. Many even move on retrograde orbits, travelling in the opposite direction to the spin and orbital motion of their hosts. And they are located much farther from their planet than their regular cousins.

Where do the irregulars come from?

Because of their wild orbits, the irregular moons cannot have formed in the same way as their regular cousins. Instead, they are thought to have been captured by their host planets as the process of planet formation came to an end.

We think that each giant planet captured just a handful of irregular moons – a number far smaller than we see today. Over the billions of years since, those moons were pummelled and destroyed by passing asteroids and comets, and collisions with other members of their swarm.

The shattered fragments of those ancient satellites form families of smaller moons – the irregulars we see today. For example, among Jupiter’s satellites we see at least four distinct families of irregular moons, each named after their largest member.

The motion of Jupiter’s irregular moons around the giant planet. The main plot (bottom, left) shows the orbits looking top-down, while the other (right and top) plots show the movement out of the plane of the system. Moons of the same colour are members of the same family.
Christopher Tylor

What does the new discovery add to our understanding?

If we consider Jupiter’s moons in terms of their orbital distance, and the direction in which they move, we can break them into three distinct groups.

The first consists of the inner eight moons, including the famous Galilean moons Io, Europa, Ganymede and Callisto, whose orbits lie in the plane of Jupiter’s equator, at distances less than 2 million kilometres.

The second group lies significantly farther from the planet, and move on orbits tilted by between 25° and 56° relative to Jupiter’s equator. These are the prograde irregulars – ten moons orbiting at distances between 7 million and 19 million km. Two of the new discoveries are members of this group.

The final and most populous group is the retrograde irregulars – 60 moons located between 19 million and 29 million kilometres from Jupiter, all moving on orbits inclined by between about 140° and 170° to Jupiter’s equator.

In other words, they orbit backwards, in the opposite direction to everything else. Nine of the new discoveries fall into this category.

Plot showing the three groups of moons orbiting Jupiter.
Carnegie Institution for Science/Roberto Molar-Candamosa

So that covers 11 of our new moons. What of the 12th? Well, it turns out that the most exciting of the new moons is an oddball – an object that does not fit into any of the groups mentioned above.

The oddball: Valetudo

The 12th new moon has tentatively been named Valetudo, after Jupiter’s mythological great granddaughter.

Valetudo is the dimmest of the newly discovered moons. At just a kilometre in diameter (or less), it is the smallest Jovian moon found to date.

The yellow lines point to the tiny moving speck of light, the newly discovered moon Valetudo.
Carnegie Institute for Science

In terms of its orbital distance, Valetudo lies bang in the middle of the retrograde irregulars – some 24 million kilometres from the giant planet. But its orbit is prograde – meaning that it moves in the direction of Jupiter’s rotation, and in the opposite direction to all other satellites in its vicinity.

Valetudo’s size and unusual orbit pose interesting questions.

How did something so small survive in the celestial firing range around Jupiter?

Could Valetudo be the final surviving remnant of a previously uncharted family, whittled to nothing by aeons of headlong flight into the retrograde irregulars?

Are there are other members of the Valetudo family out there, awaiting discovery?

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Beyond these questions, Valetudo’s small size offers an important clue to the origin of the Jovian satellite system. Had Valetudo been on its current orbit while Jupiter was still accreting, it would have been too small to resist the drag of the inflowing gas. Like a ping pong ball in a gale, it would have been dragged inwards, to be devoured by the giant planet.

In other words, tiny Valetudo tells us that the process that created the irregular satellite families continued long after the formation of Jupiter was complete. In fact, that process likely continues even now, with occasional collisions tearing moons asunder, to birth new families of irregular worlds.

Who knows? The next such collision might come when Valetudo runs into one of the retrograde irregulars. Given that their orbits cross, it may only be a matter of time.

Jonti Horner, Professor (Astrophysics), University of Southern Queensland and Christopher C.E. Tylor, PhD Candidate, Adjunct Lecturer, Assistant Examiner, University of Southern Queensland

This article was originally published on The Conversation. Read the original article.